A unit process which is frequently encountered in petroleum refining is paraffin isomerization. Paraffin isomerization of linear (straight chain) paraffins produces branched chain paraffins. In such a process, as conventionally operated, low molecular weight C.sub.4 -C.sub.6 paraffins are converted to iso-paraffins in the presence of an acidic catalyst such as aluminum chloride. Recently, C.sub.6 +, preferably C.sub.10 + n-paraffins, have been isomerized, in the presence of large pore size zeolites to produce branched chain paraffins by skeletal rearrangement. The latter process can find application in dewaxing.
Isomerization is one of several reactions which occur in reforming of naphthas. Reforming of naphthas is undertaken to upgrade a low octane naphtha to a higher octane effluent. One of the octane enhancing reactions which occurs during reforming is the isomerization of n-paraffins to isoparaffins. Under the process conditions of reforming, other reactions which occur are aromatization (or dehydrocyclization), dehydrogenation, with some cracking.
Paraffin isomerization catalysts may also be employed as ring opening catalysts for removal of cyclic aromatic precursors from reformer feedstocks. For example, cyclohexane, a precursor to benzene, is rearranged over commercial paraffin isomerization catalysts to a mixture of branched paraffins. Branched paraffins are only partly aromatized in reforming whereas cyclohexane is completely converted to aromatics, mostly benzene. Application of paraffin isomerization catalysts for ring opening aromatics precursors will no doubt become more important as environmental regulations limiting aromatics in gasoline become more stringent.